1. Field of the Invention
This invention relates generally to halogen infrared lamps with reflective coatings on the lamp envelope. More particularly, this invention relates to halogen infrared lamps coated with an infrared reflective coating substantially surrounding the entire envelope along with a totally reflecting coating disposed on ends of an ellipsoidal portion of the envelope.
2. Discussion of the Art
Improving the efficiency of lamps is increasingly important due to the rising cost of energy. Infrared reflective filters, a form of interference filters, have been used to improve the energy efficiency of lamps by reflecting infrared radiation towards the filament to heat the filament and thus increase the efficacy of the lamp. Interference filters have also been used to selectively reflect or transmit light radiation from certain portions of the electromagnetic radiation spectrum such as ultraviolet, visible, and infrared radiation. Interference filters have been used to allow a portion of the visible radiation to transmit through the envelope and reflecting the unwanted visible radiation to produce colored light.
A halogen infrared (HIR) lamp uses an infrared (IR) reflective coating on an elliptical surface of a double ended quartz halogen lamp to preferentially reflect IR radiation to a filament. This coating, however, allows some IR radiation to pass since the reflectivity in the IR region is not one hundred percent. Metal halide discharge lamps have used reflective end-coats to improve the efficacy of lamps by heating up the ends where a metal halide pool forms, thereby increasing the vapor pressure of the pool and therefore the efficacy. Moreover, computer modeling has uncovered that in HIR lamps, IR radiation is preferentially lost at particular angles as measured from the radial axis formed along the filament. If an HIR lamp recaptures the IR radiation lost at these particular angles by using an additional reflective end-coating, similar to metal halide discharge lamps, it is believed that the efficacy of the lamp can be improved.